Fluorine-containing conductive films

ABSTRACT

An atomic layer deposition (ALD) process for depositing a fluorine-containing thin film on a substrate can include a plurality of super-cycles. Each super-cycle may include a metal fluoride sub-cycle and a reducing sub-cycle. The metal fluoride sub-cycle may include contacting the substrate with a metal fluoride. The reducing sub-cycle may include alternately and sequentially contacting the substrate with a reducing agent and a nitrogen reactant.

REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/255,799, filed Apr. 17, 2014, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The application relates generally to the field of semiconductor devicemanufacturing and more particularly to methods for formingfluoride-containing conductive thin films.

Description of the Related Art

Atomic layer deposition (ALD) is based on sequential, self-saturatingsurface reactions, which can provide good conformality and step coverageregardless of the geometry of the structure to be coated. However,deposition of metallic films by ALD has been challenging, in partbecause ALD is based essentially on thermodynamically favorablehalf-reactions.

Refractory metal conducting layers are basic building blocks in microand nano-electronics. Oxidation resistant metal thin films are desirablein a number of contexts. For example, titanium nitride layers arecommonly used in the semiconductor manufacturing industry, for example,as a gate electrode material or as a copper diffusion barrier. However,titanium nitride is known to oxidize from the surface when stored inair, likely through grain boundaries, up to depths of tens ofnanometers.

SUMMARY OF THE INVENTION

In one aspect, atomic layer deposition (ALD) processes are provided fordepositing conductive fluorine-containing thin films. In someembodiments the ALD processes may comprise a plurality of super-cycles,where at least one super-cycle comprises two sub-cycles: a metalfluoride sub-cycle and a second sub-cycle. In some embodiments, themetal fluoride sub-cycle comprises contacting the substrate with a metalfluoride, and the second sub-cycle comprises alternately andsequentially contacting the substrate with a silane or borane and anitrogen reactant. In some embodiments the second sub-cycle is referredto as a reducing sub-cycle and the substrate is contacted with areducing agent and a nitrogen reactant.

According to some embodiments, the metal fluoride comprises a metalselected from Ti, Ta, Nb, Mo and W. In some embodiments, the metalfluoride comprises TiF₄. In some embodiments, the reducing agent is asilane or borane. In some embodiments, the reducing agent comprisesdisilane or trisilane. In some embodiments, the reducing agent comprisesdiborane or triborane. In some embodiments, the nitrogen reactant isselected from the group consisting of ammonia, N₂H₄, nitrogen atoms,nitrogen containing plasma and nitrogen radicals. In some embodiments,the metal fluoride is TiF₄ and the reducing agent is Si₃H₈ In someembodiments, the metal fluoride sub-cycle and the reducing sub-cycle arecarried out at a ratio of at least about 0.1 in at least one of theplurality of super-cycles. In some embodiments, the fluorine containingthing film comprises TiF₃.

According to some embodiments of a process for forming afluorine-containing thin film, the fluorine containing thin filmcomprises about 0.4 to about 2.3 at % silicon. In some embodiments, thefluorine containing thin film comprises about 5 to about 40 at %nitrogen. In some embodiments, the fluorine containing thin film isconductive. In some embodiments, the fluorine-containing thin film has alayer resistivity of less than about 10⁶ μΩcm. In some embodiments, thefluorine containing thin film is not oxidized by an air ambient at lessthan about 300° C.

According to some embodiments, there is disclosed herein a conductive,fluoride thin film comprising TiF₃. In some embodiments, the thin filmcomprises about 5 to about 40 at % nitrogen. In some embodiments, thethin film comprises about 0.4 to about 2.3 at % silicon. In someembodiments, the thin film has a thickness of less than about 100 nm. Insome embodiments, the thin film has a thickness of less than about 10nm.

According to some embodiments, there is disclosed herein an ALD processfor depositing a fluorine-containing thin film on a substrate, theprocess comprising a plurality of super-cycles, each super-cyclecomprising a metal fluoride sub-cycle and a second sub-cycle. In someembodiments, the metal fluoride sub-cycle comprises contacting thesubstrate with a metal fluoride. In some embodiments, the secondsub-cycle comprises contacting the substrate with a nitrogen reactant.In some embodiments, at least one of a silane compound and a boranecompound is separately provided in at least one of the metal fluoridesub-cycle and the second sub-cycle.

In some embodiments of an ALD process, at least one of a silane compoundand a borane compound is provided in the metal fluoride sub-cycle. Insome embodiments, at least one of a silane compound and a boranecompound is provided in the second sub-cycle. In some embodiments, thefluorine-containing thin film achieved by the process has a thickness ofless than about 100 nm. In some embodiments, at least one of the silanecompound, borane compound, and nitrogen reactant reduces at least someof the metal of the metal fluoride. In some embodiments, thefluorine-containing thin film achieved by the process comprises TiF₃. Insome embodiments, the fluorine-containing thin film achieved by theprocess exhibits a layer resistivity of less than about 10⁶ μΩcm. Insome embodiments, the fluorine-containing thin film achieved by theprocess exhibits substantially no oxidation at temperatures below about300° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the detailed descriptionand from the appended drawings, which are meant to illustrate and not tolimit the invention, and wherein:

FIG. 1 is a flow chart illustrating an ALD process for depositing aTiF₃/TiN film according to one embodiment.

FIG. 2 shows the XRD pattern of a film formed according to oneembodiment of the present disclosure.

FIG. 3 is an analysis of the oxidation behavior of a film formedaccording to one embodiment of the present disclosure.

FIG. 4 is an additional analysis of the oxidation behavior of a filmformed according to one embodiment of the present disclosure.

FIGS. 5A-C show XRD patterns of 100 cycles of pure ALD-W films depositedon TiN (FIG. 5A), SiO₂ (FIG. 5B) and HfO₂ (FIG. 5C) surfaces.

FIGS. 6A and B show XRD patterns of Ti_(x)W_(y)N_(z) films depositedusing different TiN/W cycle ratios.

FIG. 7 shows a comparison of the morphology of W_(x)N_(y) andTi_(x)W_(y)N_(z) layers deposited with various ratios of TiN to Wdeposition cycles, as well as pure W and TiN.

FIG. 8 shows SEM images of a W_(0.9)N_(0.1) (TiN/W cycle ratio=1) filmdeposited in a 3D trench structure. The grain size was too small to bedetected with SEM. The conformality and step coverage of the filmappears to be excellent.

FIGS. 9A and B show heated stage XRD patterns of aTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) film in nitrogenatmosphere. No signs of grain coarsening with heating up to 875° C. areseen. FIG. 9B shows a comparison of the film with a pure TiN film havinga similar thickness.

DETAILED DESCRIPTION

As discussed herein, fluorine-containing conductive thin films can bedeposited by vapor deposition processes, for example by atomic layerdeposition (ALD). Such films can desirably be oxidation resistant.Titanium fluoride (TiF₃) is a stable, solid fluoride that can be used ina variety of contexts, for example as a catalyst; however, deposition oftitanium fluoride films by vapor deposition processes has not previouslybeen achieved.

The presence of fluorine in some metal thin films enhances oxidationresistance. Metal nitrides, such as titanium nitride, are commonly usedin the semiconductor industry, for example as barrier films. However, asdiscussed above titanium nitride films can be subject to undesirableoxidation. The present application is based, in part, on the unexpectedfinding that a conductive thin film comprising metal fluoride, such as aconductive thin film comprising titanium fluoride, can be deposited byALD. In some embodiments the titanium fluoride-containing film hasgreater oxidation resistance than a TiN film, such as a TiN filmdeposited by known vapor deposition processes, for example by ALD.

The conductive fluorine-containing films may be used in a variety ofcontexts. For example, a conductive fluoride film, or a conductive filmcomprising metal fluoride, such as a conductive thin film comprisingTiF₃, may be used as an oxygen barrier film over a TiN layer or othermetallic film. In some embodiments conductive fluorine-containing filmsformed according to the present disclosure would be useful as a barrierfilm against ashing or other oxidative conditions. In some embodiments,conductive fluorine-containing films formed according to the presentdisclosure may be used as a protective layer against ambientenvironments comprising oxygen, such as ambient air and/or water ormoisture. In some embodiments, the conductive, fluorine-containing filmsof the present disclosure are useful as sacrificial layers, such as inpatterning layers or in other applications where good oxidationresistance is desired. In some embodiments, a conductive fluoride thinfilm is deposited conformally over vertical and horizontal surfaces. Insome embodiments, a conductive film comprising metal fluoride can beused as a p-type capping layer on a gate stack, for example on top ofhigh-k layer, such as HfO₂, and below an actual gate electrode layer ora conductive gate dielectric barrier layer. In some embodiments, when aconductive film comprising metal fluoride is used as a p-type cappinglayer, the effective work function of the electrode in the stack isabove about 4.9 eV, preferably between about 5.0 and about 5.2 eV.

In some embodiments, the conductive fluorine-containing film does notcomprise one or more of the following materials: MgF₂, CaF₂, ZnF₂, SrF₂,YF₃, or LaF₃. In some embodiments, the conductive fluorine-containingfilm does not comprise one or more of the following materials: AlF₃ orLiF. In some embodiments, the conductive fluorine-containing film doesnot comprise one or more of the following materials: alkali metalfluorides (group 1 in periodic table of elements), such as KF oralkaline earth (group 2 in periodic table of elements) metal fluorides,such as MgF₂ or CaF₂. In some embodiments, the conductivefluorine-containing film does not comprise one or more of the followingmaterials: group 3 metal fluorides, such as YF₃ or LaF₃. In someembodiments, the conductive fluoride film does not comprise more thanabout 20 at %, preferably more than about 10 at %, more preferably morethan about 5 at %, and most preferably more than about 1 at % of one ormore of the following metals: alkali metals, alkaline earth metals, andgroup 3 metals. In some embodiments, the conductive fluorine-containingfilm does not comprise more than about 20 at %, preferably more thanabout 10 at %, more preferably more than about 5 at %, and mostpreferably more than about 1 at % of one or more of the followingmetals: Mg, Ca, Zn, Sr, Y, or La. In some embodiments, the conductivefluorine-containing film does not comprise more than about 20 at %,preferably more than about 10 at %, more preferably more than about 5 at%, and most preferably more than about 1 at % of metals other than oneor more of the following metals: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, or W,and preferably metals other than one or more of the following metals:Ti, Nb, Ta, Mo, and W.

In some embodiments, ALD processes are provided for depositing aconductive film comprising metal fluoride on a substrate. In someembodiments, the processes may comprise a first sub-cycle in which thesubstrate is exposed to a vapor phase metal fluoride, such as TiF₄, anda monolayer of metal fluoride is adsorbed on the substrate surface. In asecond sub-cycle, a vapor phase silane or borane compound, or other“reducing agent”, and a vapor phase nitrogen reactant are alternatelyand sequentially provided. The reducing agent and nitrogen reactantreact with the metal fluoride on the substrate surface to form aconductive film comprising metal fluoride. In some embodiments, a firstsub-cycle may include both a vapor phase metal fluoride, such as TiF₄,and a reducing agent, such as a silane or a borane. In some embodiments,a second cycle does not include a silane or a borane. Thus, in someembodiments, a first cycle comprises a vapor phase metal fluoride and asilane or a borane, and a second cycle comprises a vapor phase nitrogenreactant. Although the term “reducing agent” is used, in someembodiments, chemical reduction is not required. Thus, in someembodiments the term “reducing agent” simply represents a silanecompound or a borane compound. However, without being bound to anytheory, it is believed that in some embodiments, a reducing agent asherein described might reduce the oxidative state of a metal species onthe surface.

In some embodiments the metal may be selected from Ti, Ta, Nb, Mo, andW, for example. The reducing agent may be, for example, a silane orborane compound. The nitrogen reactant may be, for example, NH₃. In someembodiments where a nitrogen reactant is used, the nitrogen reactant mayexhibit at least some reducing effect on the oxidation state of a metalspecies on the substrate surface.

The first and second sub-cycles together make an ALD super-cycle. Ineach super-cycle, the first sub-cycle and the second sub-cycle may beindependently repeated one or more times. Further, the super-cycle maybe repeated one or more times to deposit a conductive film comprisingmetal fluoride to a desired thickness. The first and second sub-cyclescan be performed in any order. For example, in some embodiments thesecond sub-cycle may be performed first. Moreover, the order of thereactants in each sub-cycle may be varied. For example, in someembodiments, in the reducing sub-cycle—which may be performed first orsecond—the nitrogen reactant is pulsed before the silane or boranecompound or vice versa.

The ratio of the first sub-cycle to the second sub-cycle within one ormore super-cycles can be varied to deposit a film with a desiredcomposition and/or desired properties. In some embodiments the ratio ofthe first sub-cycle to the second sub-cycle is the same in eachsuper-cycle in the ALD process. In some embodiments the ratio of firstsub-cycles to second sub-cycles may vary in one or more super-cyclesduring the deposition process.

In some embodiments a conductive thin film comprising metal fluoride isformed that comprises some silicon or boron from the reducing compoundand/or some nitrogen from the nitrogen reactant. For example, in someembodiments a conductive thin film comprising TiF₃ is deposited thatcontains some Si and some N.

All atomic percentage (i.e., at %) values provided herein excludehydrogen for simplicity and because hydrogen is difficult to accuratelyanalyze quantitatively.

In some embodiments, a silane is used as a reducing agent and theconductive film comprising metal fluoride also comprises a small amountof silicon. For example, in some embodiments, the silicon content may beless than about 15 at %. In some embodiments the silicon content may befrom about 0.01 to about 10 at %, from about 0.1 to about 5 at %, orfrom about 0.1 to about 2 at %. In some embodiments, the silicon contentin a conductive film comprising metal fluoride is preferably less thanabout 1.5 at %.

In some embodiments a borane is used as a reducing agent and theconductive film comprising metal fluoride also comprises a small amountof boron. For example, in some embodiments, the boron content may beless than about 15 at %. In some embodiments the boron content is fromabout 0.01 to about 10 at %, from about 0.1 to about 5 at %, or fromabout 0.1 to about 2 at %. In some embodiments, the boron content isless than about 1.5 at %.

In some embodiments, the films comprise a small amount of nitrogen. Forexample, in some embodiments, the nitrogen content may range from about0.5 to about 50 at %, from about 1 to about 20 at %, or from about 2 toabout 15 at %.

In some embodiments, the films comprise fluorine in an amount greaterthan about 10 at %, from about 20 to about 75 at %, from about 40 toabout 70 at %, or from about 45 to about 65 at %.

In some embodiments, the films have a fluorine to titanium ratio (F/Ti(at %/at %)) of from about 0.25 to about 5, from about 0.5 to about 3,or from about 1 to about 2.5.

In some embodiments, the films may comprise a small amount of oxygen,despite the fact that the films are oxidation resistant. For example, insome embodiments, the oxygen content is less than about 2.5 at %, lessthan about 1.5 at %, less than about 1.0 at %, or even less than about0.5 at %.

In some embodiments a conductive film comprising metal fluoride anddeposited by an ALD process as described herein has a greater oxidationresistance than a corresponding metal nitride film deposited by a knownvapor deposition process, such as by ALD.

In some embodiments, the metal fluoride films have a good smoothness,which can reduce or prevent oxidation of an underlying film, for examplea TiN film beneath a layer comprising TiF₃. In some embodiments, oxygendiffusion or oxidation of a film comprising metal fluoride does notproceed as deep as in an underlying film, such as an underlying TiNlayer.

In some embodiments a conductive thin film comprising TiF₃ is depositedby an ALD process comprising a first sub-cycle for adsorbing TiF₄ on asubstrate surface in a self-limiting manner and a second sub-cycle forreducing the TiF₄ to TiF₃. For example TiF₄ may be provided in a firstsub-cycle such that up to a monolayer of TiF₄ forms on a substratesurface. The first sub-cycle may be repeated two or more times. In someembodiments, a purge step is included between respective firstsub-cycles. In the second sub-cycle the substrate is alternately andsequentially exposed to a reducing agent, such as a silane or a boranecompound, and a nitrogen reactant, such as ammonia. The second sub-cycleserves to reduce at least a portion of the TiF₄ on the substrate surfaceto TiF₃. In some embodiments, the films formed comprise TiF₃ withrelatively small amounts of silicon or boron and nitrogen. In someembodiments, the films formed comprise a mixture of TiF₃ and somenitrogen. In some embodiments the film is a mixture of TiF₃ and TiN.

Each of the first and second sub-cycles may be repeated one or moretimes in a super-cycle. The super-cycle is repeated until a film of thedesired thickness is achieved. By adjusting the ratio of the twosub-cycles in one or more super-cycles, the quantity of TF₃ can beincreased without introducing an undesirable amount of silicon ornitrogen. In particular, in some embodiments increasing the number ofsecond sub-cycles in which the substrate is alternately and sequentiallycontacted with the reducing agent and the nitrogen reactant, relative tothe first sub-cycle, increases the amount of TiF₄ that is converted toTiF₃.

In some embodiments the reducing (second) sub-cycle may utilize asilicon compound; however, other compounds may be used. In someembodiments, the silicon compound is a silane compound, such as SiH₄,Si₂H₆, or Si₃H₈. In some embodiments, a boron compound may be used in atleast one reducing sub-cycle. For example, in some embodiments, thereducing agent may be a borane compound, such as one or more of BH₃,B₂H₆, or triborane. It will be appreciated that other reducing agentsmay also be used. In some embodiments the same reducing agent is used ineach sub-cycle, while in other embodiments different reducing agents maybe utilized in one or more sub-cycles.

In some embodiments the nitrogen reactant may comprise one or more ofNH₃, nitrogen atoms, nitrogen radicals, nitrogen plasma, other excitedspecies comprising nitrogen that can, for example, be generated by aplasma, or other suitable nitrogen-containing compounds.

In some embodiments a conductive thin film comprising TiF₃ is depositedthat has a greater oxidation resistance than a TiN film deposited byknown vapor deposition processes that do not incorporate fluorine in thefilm, such as a TiN film deposited by ALD.

In some embodiments a conductive thin film comprising fluorine, such asa metal fluoride thin film comprising at least some nitrogen, isdeposited that is smooth and does not have a columnar grain structure.In some embodiments, the film has grain structure or morphology thatdoes not have many or too much substantial grain boundaries, for examplecompared to normal ALD TiN films, which also tends to suppress theoxidation of the film. In some embodiments the conductive thin filmcomprising fluorine has fewer grain boundaries than a TiN film depositedby ALD.

In some embodiments a conductive thin film comprising TiF₃ with athickness of about 500 nm or less is deposited. In some embodiments thethin film has a thickness of less than about 100 nm, less than about 50nm, or less than about 10 nm. In some embodiments the thickness can beselected depending on the application where the film would be used. Forexample where the film is to serve as a p-type capping layer or as anoxidation prevention layer, the thickness of the film could be much lessthan described above, for example, from about 2 to about 50 Å, fromabout 3 to about 30 Å, and in some cases from about 5 to about 20 Å.

In some embodiments, the conductive, thin film comprising fluorine, sucha metal fluoride thin film comprising at least some nitrogen, is not ananolaminate and separate layers of metal fluoride and metal nitride arenot visible. In some embodiments less than about 60 or less than about40 consecutive metal fluoride deposition sub-cycles (MF) are carried outin a super-cycle. In some embodiments less than about 10 or less thanabout 5 consecutive reducing sub-cycles are carried out in asuper-cycle.

For example, in some embodiments a conductive thin film comprising TiF₃is not a nanolaminate film or a film in which distinct and separatelayers of titanium fluoride and titanium nitride are observable.

While illustrated primarily in the context of forming conductive thinfilms comprising TiF₃, other metal fluoride films or films containing atleast some fluorine can be deposited using an ALD super-cycle comprisingat least one sub-cycle in which a metal fluoride reactant is utilized.For example in some embodiments a metal nitride film comprising twodifferent metals and fluorine may be deposited by an ALD processcomprising a first sub-cycle in which a substrate is alternately andsequentially contacted with a first metal reactant and a first nitrogenreactant and a second sub-cycle in which the substrate is alternatelyand sequentially contacted with a metal fluoride and a reducing agent,such as a silane or borane. Exemplary processes are described, forexample, in U.S. application Ser. No. 13/802,157, which is incorporatedby reference herein in its entirety.

In some embodiments methods a provided for depositing an M¹ _(x)M²_(y)N_(z) film, where M¹ and M² are different metals, and may beselected, for example, from Ti, Ta, Nb, Mo, and W. In some embodimentsthe methods comprise a first ALD sub-cycle in which a first metalnitride is deposited by alternately and sequentially contacting asubstrate with a metal precursor, such as a metal halide, and a nitrogenreactant, such as NH₃, and a second ALD sub-cycle in which elementalmetal is deposited by alternately and sequentially contacting thesubstrate with a second, different metal fluoride reactant and a secondreactant, such as Si₂H₆. The two sub-cycles together form a super-cyclethat can be repeated as many times as desired to achieve a film of anappropriate thickness for a particular application. Within eachsuper-cycle, the ratio of metal nitride to metal sub-cycles can beadjusted to achieve a desired film composition and properties. In someembodiments, the surface of the M¹ _(x)M² _(y)N_(z), film comprisesabout 0.5 at % to about 10 at % fluorine. In some embodiments, theentire M¹ _(x)M² _(y)N_(z), film comprises about 0.1 at % to about 5 at%, preferably from about 0.3 at % to about 4 at % fluorine.

In some embodiments, methods of forming a Ti_(x)W_(y)N_(z) film comprisea first ALD sub-cycle in which titanium nitride is deposited byalternately and sequentially contacting a substrate with a titaniumprecursor, such as TiCl₄ and a nitrogen reactant, such as NH₃, and asecond ALD sub-cycle in which tungsten is deposited by alternately andsequentially contacting the substrate with a tungsten fluoride reactant,such as WF₆ and a second reducing reactant, such as Si₂H₆. The nitrogenand reducing reactants can be as described elsewhere herein. The twosub-cycles together form a super-cycle that can be repeated as manytimes as desired to achieve a thin film comprising fluorine, of anappropriate thickness for a particular application. Within eachsuper-cycle, the ratio of TiN to W sub-cycles can be adjusted to achievea desired film composition and properties.

The ALD processes described herein can be used to deposit filmscomprising metal fluoride, which can be referred to as MF films, such asfilms comprising titanium fluoride. The stoichiometry, and thus therelative amounts of M and F can vary. For example, the relative amountsof Ti and F in a film comprising titanium fluoride can vary. Further, asdiscussed above, in some embodiments the films can comprise twodifferent metals. The amount of each element in the film can becontrolled, for example by controlling the ratio of the sub-cycles inthe deposition processes.

For example, in some embodiments for forming conductive films comprisingTiF₃, increasing the number of reducing sub-cycles relative to thetitanium fluoride sub-cycles may reduce the amount of TiF₄ in the filmwhile increasing the amount of TiF₃ in the film. In some embodiments,the titanium fluoride to reducing sub-cycle ratio is less than or equalto about 1 and TiF₃ films with a nitrogen content of less than about 10at.-% can be produced. As the titanium fluoride to reducing sub-cycleratio increases, the amount of fluoride generally in the film increasesand the relative TiF₃ content increases and the nitrogen content mayalso decrease. Without being bound to any theory, it is believed that insome circumstances a solid solution may be formed. In some embodimentsthis may lead to a phenomenon called solid solution strengthening.

Atomic Layer Deposition (ALD)

ALD type processes are based on controlled, self-limiting surfacereactions of precursor chemicals. Gas phase reactions are avoided byfeeding the precursors alternately and sequentially into the reactionchamber. Vapor phase reactants are separated from each other in thereaction chamber, for example, by removing excess reactants and/orreactant by-products from the reaction chamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure. Insome embodiments the substrate comprises a 300 mm silicon wafer. In someembodiments the substrate comprises a 450 mm wafer. Depositiontemperatures are maintained below the precursor thermal decompositiontemperature but at a high enough level to avoid condensation ofreactants and to provide the activation energy for the desired surfacereactions. Of course, the appropriate temperature window for any givenALD reaction will depend upon the surface termination and reactantspecies involved.

A first reactant is conducted or pulsed into the chamber in the form ofvapor phase pulse and contacted with the surface of a substrate.Conditions are preferably selected such that no more than about onemonolayer of the precursor is adsorbed on the substrate surface in aself-limiting manner. Excess first reactant and reaction byproducts, ifany, are purged from the reaction chamber, often with a pulse of inertgas such as nitrogen or argon.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, more preferably betweenabout 1 and 10, and still more preferably between about 1 and 2 seconds.However, other purge times can be utilized if necessary, such as whendepositing layers over extremely high aspect ratio structures or otherstructures with complex surface morphology is needed. The appropriatepulsing times can be readily determined by the skilled artisan based onthe particular circumstances.

A second gaseous reactant is pulsed into the chamber where it reactswith the first reactant bound to the surface. Excess second reactant andgaseous by-products of the surface reaction are purged out of thereaction chamber, preferably with the aid of an inert gas. The steps ofpulsing and purging are repeated until a thin film of the desiredthickness has been formed on the substrate, with each cycle leaving nomore than a molecular monolayer. In forming metal fluoride films, suchas TiF₃ films, two sub-cycles are repeated one or more times in each ALDsuper-cycle.

Additional reactants can also be supplied that aid in the depositionprocess. Such reactants can be provided either in their own pulses oralong with precursor pulses, and can be used for example to provide adesired surface termination, or to strip or getter adhered ligandsand/or free by-product. In some embodiments the additional reactants donot contribute any species to the growing film.

The precursors employed in the processes may be solid, liquid, orgaseous material under standard conditions (room temperature andatmospheric pressure), provided that they are in vapor phase before theyare conducted into the reaction chamber and contacted with the substratesurface.

As mentioned above, each pulse or phase of each cycle or sub-cycle ispreferably self-limiting. An excess of reactant precursors is suppliedin each phase to saturate the susceptible structure surfaces. Surfacesaturation ensures reactant occupation of all available reactive sites(subject, for example, to physical size or “steric hindrance”restraints) and thus provides excellent step coverage. In somearrangements, the degree of self-limiting behavior can be adjusted by,e.g., allowing some overlap of reactant pulses to trade off depositionspeed (by allowing some CVD-type reactions) against conformality. IdealALD conditions with reactants well separated in time and space providenear perfect self-limiting behavior and thus maximum conformality, butsteric hindrance results in less than one molecular layer per cycle.Limited CVD reactions mixed with the self-limiting ALD reactions canraise the deposition speed.

“Pulsing” a vaporized reactant onto the substrate means that the vaporis conducted into the chamber for a limited period of time. Typically,the pulsing time is from about 0.05 seconds to about 10 seconds.However, depending on the substrate type and its surface area, thepulsing time may be even higher than about 10 seconds.

As an example, for a 300 mm wafer in a single wafer ALD reactor, theprecursors are typically pulsed for from about 0.05 seconds to about 10seconds, more preferably for from about 0.1 seconds to about 5 secondsand most preferably for from about 0.3 seconds to about 3.0 seconds.However, pulsing times can be on the order of minutes in some cases. Theoptimum pulsing time can be readily determined by the skilled artisanbased on the particular circumstances.

The mass flow rate of the metal precursor can be determined by theskilled artisan. In some embodiments, for example for deposition on 300mm wafers, the flow rate of the reactants is preferably between about 1sccm and about 1000 sccm, about 10 sccm to about 800 sccm, or about 50sccm to about 500 sccm, without limitation.

The pulsing time and mass flow rate of each of the reactants can beselected independently. In some embodiments the pulsing time (and/ormass flow rates) of two or more of the reactants is the same, while insome embodiments the pulsing times (or mass flow rates) are different.

The pressure in the reaction chamber is typically from about 0.01 mbarto about 20 mbar, more preferably from about 1 mbar to about 10 mbar.However, in some cases the pressure will be higher or lower than thisrange, as can be readily determined by the skilled artisan depending onmultiple parameters, such as the particular reactor being used, theprocess and the precursors.

Before starting the deposition of the film, the substrate may be heatedto a suitable growth temperature, as discussed above. The preferreddeposition temperature may vary depending on a number of factors suchas, and without limitation, the reactant precursors, the pressure, flowrate, the arrangement of the reactor, and the composition of thesubstrate including the nature of the material to be deposited on. Thespecific growth temperature may be selected by the skilled artisan basedon the particular circumstances.

In some embodiments, the deposition temperature is about 100° C. toabout 700° C., about 200° C. to about 500° C., about 250° C. to about400° C., or about 325° C. to about 375° C.

The processing time depends, in part, on the thickness of the layer tobe produced, the composition of the film, the growth rate of theindividual deposition sub-cycles and the overall growth rate.

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400 Series reactor, available from ASM America, Inc of Phoenix,Arizona and ASM Europe B.V., Almere, Netherlands. In addition to theseALD reactors, many other kinds of reactors capable of ALD growth of thinfilms, including CVD reactors equipped with appropriate equipment andmeans for pulsing the precursors can be employed. In some embodiments aflow type ALD reactor is used.

In some embodiments the reactor is a batch reactor capable of holdingmore than about 50 substrates, more than about 100 substrates, or morethan about 125 substrates. In some embodiments the reactor is amini-batch reactor and has from 2 to about 20 substrates, from 3 toabout 15 substrates, or from 4 to about 10 substrates. In someembodiments, the substrate is a silicon wafer, such as a silicon waferhaving a diameter of at least about 150 mm. In some embodiments thesubstrate is a silicon wafer having a diameter of at least about 200mm,or at least about 300 mm. In some embodiments, the substrate could be asilicon wafer having a diameter of at least about 450 mm.

The ALD processes for depositing conductive films comprising metalfluoride described herein can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, whichimproves the throughput compared to a reactor in which the substrate isheated up to the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

Deposition of Conductive Films Comprising Metal Fluoride

As mentioned above and discussed in detail below conductive, conductivefilms comprising metal fluoride can be deposited using a metal fluoridedeposition sub-cycle and a reducing sub-cycle. In some embodiments themetal can be selected from Ti, Ta, Nb, Mo, and W. The two sub-cycles canbe repeated at a desired ratio in a super-cycle to form a smooth and/ornanocrystalline film. In some embodiments the conductive thin films,such as thin films comprising metal fluoride, do not have a columnargrain structure.

In some embodiments the deposition process is an ALD process. In someembodiments, the deposition process is a sequential or cyclic process,such as a sequential or pulsed CVD process utilizing the same precursorand conditions selections as an ALD process. In some embodiments thedeposition process is a PECVD process. In some embodiments thedeposition process is an LPCVD/RTCDV process. In some embodiments thedeposition process has a step which is not self-limiting. In someembodiments the process may operate in a process condition regime closeto CVD conditions or in some cases fully in CVD conditions.

In some embodiment a conductive thin film comprising metal fluoride isdeposited by a process that may comprise multiple super-cycles, whereeach super-cycle comprises at least one MF (metal fluoride) sub-cycleand at least one reducing sub-cycle. The ratio of the MF and reducingsub-cycles in each super-cycle can be varied to achieve the desiredcomposition, and the number of super-cycles can be selected to deposit afluorine-containing film of the desired thickness. In some embodiments,the number of each sub-cycle conducted consecutively in a super-cycle islimited such that a homogenous conductive thin film, such as a aconductive film comprising metal fluoride, is formed, where distinctlayers of MF and MN are not visible, for example, in a cross-section TEMor SEM image.

The super-cycle can be written as:

a[b(MF)+c(reducing agent+nitrogen compound)], where MF represents aM_(x)F_(y) sub-cycle and b is the number of MF sub-cycles in eachsuper-cycle; (reducing agent+nitrogen compound) represents the reducingsub-cycles and c is the number of reducing sub-cycles in eachsuper-cycle; and a is the number of super-cycles. The ratio of metalfluoride to reducing sub-cycles can be given as b: c.

The first and second deposition sub-cycles (b and c) may be provided ata selected ratio to deposit a thin film with a desired composition anddesired properties. For example, in some embodiments, the ratio of thefirst, metal fluoride deposition sub-cycle to the second reducingsub-cycle (b:c) in one or more super-cycles may be from about 0.01 toabout 100, about 0.05 to about 50 or about 0.1 to about 1. In someembodiments, the ratio of metal fluoride adsorption sub-cycles toreducing sub-cycles in one or more super-cycles is less than one. Insome embodiments, the ratio of metal fluoride adsorption sub-cycles toreducing sub-cycles in one or more super-cycles is between about 1 andabout 3. In some embodiments, the ratio of metal fluoride adsorptionsub-cycles to reducing sub-cycles in one or more super-cycles is betweenabout 1 and about 50, between about 3 and about 30 or between about 5and about 20. In some embodiments, the ratio of metal fluorideadsorption sub-cycles to reducing sub-cycles in one or more super-cyclesis about 0.5, about 1, about 3, about 5, about 10, about 20, about 40 orabout 50.

In some embodiments, the ratio of first metal fluoride adsorptionsub-cycles to second reducing sub-cycles (b: c) is the same in all ofthe complete super-cycles performed in the process. In otherembodiments, the specific ratio of first metal fluoride adsorptionsub-cycles to second reducing sub-cycles can be varied in differentcomplete super-cycles. The specific ratios can be selected by theskilled artisan to provide the desired amounts of metal, fluoride, andnitrogen in the film and thus to achieve a film with desired properties.

Although referred to as the first metal fluoride adsorption sub-cycleand the second reducing sub-cycle, in some embodiments one or moresuper-cycles begins with the reducing sub-cycle, which is followed(after repeating a desired number of times) by the metal fluorideadsorption sub-cycle (which may also be repeated a desired number oftimes before beginning another super-cycle).

In some embodiments, the super-cycle can be written as:

a[b(MF+reducing agent)+c(nitrogen reactant)], where b is the number ofMF sub-cycles—which includes a reducing agent—in each super-cycle; c isthe number of nitrogen reactant sub-cycles in each super-cycle; and a isthe number of super-cycles. The ratio of metal fluoride to nitrogensub-cycles can be given as b:c.

In some embodiments, the metal, or M, comprises Ti, Ta, Nb, Mo, or W.

In some embodiments, the reducing agent comprises a silane or a borane.In some embodiments, the reducing agent is silane, disilane, ortrisilane. In some embodiments, the reducing agent is borane, diborane,or triborane. As mentioned above, although referred to as a “reducingagent,” in some embodiments it is not necessary that actual chemicalreduction takes place. Similarly, in some embodiments reduction does notnecessarily take place in a “reducing sub-cycle.”

In some embodiments the nitrogen-precursor can be selected from thegroup consisting of ammonia, N₂H₄, nitrogen atoms, nitrogen-containingplasma or nitrogen radicals or other species generated in a plasma.

In some embodiments a thermal ALD process is used for depositing aconductive fluoride film and the N-precursor is ammonia or N₂H₄. In someembodiments a plasma ALD process is used and the N-precursor fordepositing a conductive, fluoride-containing film comprises nitrogenatoms, nitrogen-containing plasma, or nitrogen radicals.

Specific process conditions and parameters are provided below fordeposition of exemplary conductive thin films comprising TiF₃ andfluorine-containing TiWN films, though the process conditions describedwith respect to these processes can be applied to the deposition ofother conductive films comprising fluoride.

In some embodiments, the first and second deposition sub-cycles areperformed at same reaction temperature. In some embodiments thedeposition temperature for one or both of the metal fluoride andreducing sub-cycles is about 100° C. to about 700° C., about 200° C. toabout 500° C., about 250° C. to about 400° C., or about 325° C. to about375° C. In some embodiments both the TiF₄ and reducing sub-cycles arecarried out at about 350° C.

In some embodiments the ratio of metal fluoride sub-cycles to reducingsub-cycles is selected to deposit a film that closes at very thinthicknesses, such as less than about 3 nm (where closed means that atomsof the underlying substrate are not detected at the outermost surfaceanymore, as determined, for example, by LEIS). In some embodiments theratio of sub-cycles is selected such that the film is electricallycontinuous, i.e., conducts current at very thin thicknesses, such asless than about 3 nm, less than about 2 nm, less than about 1.5 nm, oreven less than about 1.0 nm. In some embodiments the ratio of sub-cyclesis selected such that the film is continuous as a layer, but may containsome non-continuous features, such as holes, in the continuous matrix atvery thin thicknesses, such as less than about 3 nm, less than about 2nm, less than about 1.5 nm, or even less than about 1.0 nm. In someembodiments the ratio of sub-cycles is selected such that the film isnot closed and may not be continuous, but still acts as a diffusionbarrier at very thin thicknesses, such as less than about 3 nm, lessthan about 2 nm, less than about 1.5 nm, or even less than about 1.0 nm.

In some embodiments, a conductive film comprising fluoride is depositedwith an RMS roughness below about 2 nm, below about 1.5 nm, below about1.0 nm, or even below about 0.7 nm, where the thickness is from about 20to about 50 nm. However, in some embodiments the RMS roughness is belowabout 0.5 nm, below about 0.4 nm or even below about 0.3 nm for filmswith a thickness of less than about 10 nm. RMS roughness can bemeasured, for example, by x-ray reflectivity (XRR).

In some embodiments, increasing the relative number of reducingsub-cycles in each super-cycle increases the sheet resistance and/orresistivity of the metal fluoride film.

In some embodiments, a conductive fluoride-containing film formedaccording the present disclosure may have a sheet resistance of lessthan about 200,000 Ω/sq, less than about 140,000 Ω/sq, less than about20,000 Ω/sq, less than about 10,000 Ω/sq, less than about 1,000 Ω/sq, oreven less than about 1,000 Ω/sq.

In some embodiments, a conductive, fluoride-containing film formedaccording the present disclosure may have a layer resistivity of lessthan about 10⁶ μΩcm, less than about 10⁵ μΩcm, or less than about 50000μΩcm.

In some embodiments, a conductive, fluoride-containing film formedaccording the present disclosure may have a layer resistivity of atleast about 500 μΩcm, at least about 1,000 μΩcm, at least about 5,000μΩcm, or even at least about 10,000 μΩcm

In some embodiments, a film comprising metal fluoride formed accordingthe present disclosure may have exhibit substantially no oxidation attemperatures below about 500° C., below about 400° C., below about 300°C., or below about 250° C. in an atmosphere containing oxygen. In someembodiments, the films are resistant to oxidation for prolonged periodsin room temperature or temperatures naturally occurring outdoors, suchas from about -50° C. to about 50° C., in oxygen containing atmospheressuch as ambient air. For example, according to some embodiments, filmsformed according the present methods may be resistant to oxidationresistance for more than 6 hours, preferably more than 24 hours, and, insome cases, depending on the film composition, the films could beresistant to oxidation for periods of more than 10 days, preferably morethan 30 days, and, in some cases, if desired, more than 1 year. Exposureto, for example, ambient air might occur in some particularapplications, for example, in case the film comprising metal fluoride isused as protective layer against ambient air which can comprise alsomoisture/water. Other atmospheres containing oxygen could include oxygenatoms, plasma or radicals, ozone, water/moisture, or other speciescontaining OH-groups.

Deposition of Films Comprising TiF₃ by ALD

As mentioned above, in some embodiments an atomic layer depositionprocess for depositing films comprising TiF₃, such as conductive filmscomprising a TiF_(x) compound—such as TiF₃—may comprise multiplesuper-cycles, where each super-cycle comprises at least one TiF₄sub-cycle and at least one reducing sub-cycle. In the TiF₄ sub-cycle thesubstrate is exposed to vapor phase TiF₄ such that up to a monolayeradsorbs on the substrate surface. In the reducing sub-cycle thesubstrate is exposed to a reducing agent, such as a silane or borane anda nitrogen reactant. The ratio of the TiF₄ and reducing sub-cycles canbe varied to achieve the desired composition, and the number ofsuper-cycles can be selected to deposit a titanium fluoride film of thedesired thickness. The TiF₄ sub-cycle may precede the reducing sub-cycleand vice versa. Similarly, in the reducing cycle, the reducing agent mayprecede the nitrogen reactant and vice versa.

In some embodiments, the TiF₄ sub-cycle may include a reducing agent,such as a silane compound or a borane compound. And in some embodiments,the second sub-cycle does not include a silane or a borane compound.

The super-cycle can be written as:

a[b(titanium fluoride)+c(reducing agent+nitrogen reactant)], where(titanium fluoride) represents a TiF₄ sub-cycle and b is the number ofTiF₄ sub-cycles in each super-cycle; (reducing agent+nitrogen reactant)represents a reducing sub-cycle and c is the number of reducingsub-cycles in each super-cycle; and a is the number of super-cycles.Although illustrated with the TiF₄ sub-cycle coming first in thesuper-cycle, in some embodiments, in one or more super-cycles, thereducing sub-cycle comes first. Thus in some embodiments the TiF₄sub-cycle can be considered the first sub-cycle and the reducingsub-cycle can be considered the second sub-cycle, while in someembodiments the reducing sub-cycle can be considered the first sub-cycleand the TiF₄ sub-cycle can be considered the second sub-cycle.

Though, in some embodiments, the super-cycle can be written as:

a[b(TiF₄+reducing agent)+c(nitrogen reactant)], where b is the number ofTiF₄ sub-cycles—which includes a reducing agent—in each super-cycle; cis the number of nitrogen reactant sub-cycles in each super-cycle; and ais the number of super-cycles. The ratio of metal fluoride to nitrogensub-cycles can be given as b:c.

In some embodiments the reducing agent can be a borane or silane, suchas diborane, triborane, disilane, or trisilane. In some embodiments thereducing agent is disilane. In some embodiments the reducing agent istrisilane. In some embodiments the nitrogen reactant can be ammonia,N₂H₄, nitrogen atoms, nitrogen-containing plasma, or nitrogen radicals.

In some embodiments a super-cycle can be written asa[b(TiF₄)+c(Si₂H₆+NH₃)], where b is the number of TiF₄ sub-cycles ineach super-cycle, c is the number of reducing sub-cycles in eachsuper-cycle, and a is the number of super-cycles.

The ratio of TiF₄ to reducing sub-cycles can thus be given as b:c (orTiF₄:reducing). In some embodiments the ratio of sub-cycles is constantin each ALD super-cycle in the ALD process. In other embodiments theratio of sub-cycles may be changed in one or more super-cycle. Unlessindicated otherwise, when a ratio of sub-cycles is provided herein, itrefers to the ratio of sub-cycles in a complete ALD process comprisingmultiple super-cycles.

In some embodiments, the first and second deposition sub-cycles areperformed at same reaction temperature. In some embodiments thedeposition temperature for one or both of the TiF₄ and reducingsub-cycles is about 100° C. to about 700° C., about 200° C. to about500° C., about 250° C. to about 400° C., or about 325° C. to about 375°C. In some embodiments both the TiF₄ and reducing sub-cycles are carriedout at about 350° C.

In some embodiments, the first and second sub-cycles are performed inthe same reactor.

The first and second sub-cycles may be provided at a selected ratio todeposit a thin film with a desired composition and desired properties.For example, in some embodiments the ratio of the first, TiF₄ depositionsub-cycle to the second reducing sub-cycle in one or more ALDsuper-cycles may be from about 0.01 to about 100, about 0.05 to about 50or about 0.1 to about 1. In some embodiments the ratio of TiF₄deposition sub-cycles to reducing sub-cycles in one or more super-cyclesis less than one. In some embodiments, the ratio of TiF₄ depositionsub-cycles to reducing sub-cycles in one or more super-cycles is betweenabout 1 and about 3. In some embodiments the ratio of TiF₄ depositionsub-cycles to reducing sub-cycles in one or more super-cycles is betweenabout 1 and about 50, between about 3 and about 30 or between about 5and about 20. In some embodiments the ratio of TiF₄ depositionsub-cycles to reducing sub-cycles in one or more super-cycles is about0.01, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.8or about 1.

As mentioned above, the ratio of sub-cycles can be selected to achieve adesired composition and desired film properties. In some embodiments agreater percentage of the TiF₄ is converted to TiF₃ by increasing thenumber of reducing sub-cycles relative to the TiF₄ sub-cycles. In someembodiments the ratio of TiF₄ to reducing sub-cycles is increased toincrease the sheet resistance and/or resistivity of the deposited film.

In some embodiments the ratio of first TiF₄ deposition sub-cycles tosecond reducing sub-cycles is the same in all of the complete ALDsuper-cycles performed in the ALD process. In other embodiments thespecific ratio of first TiF₄ deposition sub-cycles to second reducingdeposition sub-cycles can be varied in different complete ALDsuper-cycles. The specific ratios can be selected by the skilled artisanto provide the desired amounts of titanium, fluorine, nitrogen in thefilm and thus to achieve a film with the desired properties.

In some embodiments the film comprising TiF₃ that is deposited is aconductive film. In some embodiments a film comprising TiF₃ is depositedthat has a greater oxidation resistance than a TiN film deposited byknown vapor deposition processes that do not incorporate fluorine in thefilm, such as ALD (for example as measured at 300° C. in an airambient).

In some embodiments a conductive film comprising TiF₃ is formed thatcomprises some silicon or boron from the reducing compound and somenitrogen from the nitrogen reactant. For example, in some embodiments aconductive film comprising TiF₃ is deposited that contains some Si andsome N.

In some embodiments, a silane is used as a reducing agent and the filmcomprising TiF₃ also comprises a small amount of silicon. For example,in some embodiments, the silicon content may range from about 15 at %,preferably from about 0.01 to about 10 at %, more preferably from about0.1 to about 5 at %, and most preferably from about 0.1 to about 2 at %.In some embodiments, the silicon content is preferably less than about1.5 at %.

In some embodiments a borane is used as a reducing agent and the filmcomprising TiF₃ also comprises a small amount of boron. For example, insome embodiments, the boron content may range from less than about 15 at%, from about 0.01 to about 10 at %, from about 0.1 to about 5 at %, orfrom about 0.1 to about 2 at %. In some embodiments, the boron contentis preferably less than about 1.5 at %.

In some embodiments, the films comprising TiF₃ also comprise a smallamount of nitrogen. For example, in some embodiments, the nitrogencontent may range from about 0.5 to about 50 at %, from about 1-20 at %,or from about 2 to about 15 at %.

In some embodiments, the films comprise fluorine in an amount greaterthan about 10 at %, preferably from about 20 to about 75 at %, fromabout 40 to about 70 at %, or from about 45 to about 65 at %.

In some embodiments the films comprising TiF₃ comprise less than about 1at % oxygen.

FIG. 1 illustrates an ALD process for forming a film comprising TiF₃ ona substrate in a reaction chamber comprising multiple ALD super-cycles100. Each super-cycle comprises a first TiF₄ deposition sub-cycle 200and a second reducing sub-cycle 300. The super-cycle 100 is repeated asmany times as desired to deposit a TiF₃ film of the desired thickness.The ratio between sub-cycles 200 and 300 within the super-cycle 100 maybe selected to achieve a film with the desired composition andproperties.

The first titanium fluoride deposition sub-cycle comprises:

pulsing vaporized TiF_(x), such as TiF₄, into the reaction chamber 210to form at most a molecular monolayer of titanium fluoride on thesubstrate and purging the reaction chamber 220 to remove excess titaniumfluoride and reaction by products, if any, and

repeating 250 the pulsing and purging steps.

In some embodiments, the first deposition sub-cycle is repeated 1, 2, 3,4, 5, 10, 20, 50, 100, or more times in succession. In some embodimentsthe first deposition sub-cycle is repeated no more than about 30-60times consecutively, up to about 30 to 50 times consecutively, or up toabout 40 times consecutively.

The atomic layer deposition super-cycle 100 for forming the TiF₃/TiNfilm also comprises one or more second reducing sub-cycles 300. In someembodiments, the second reducing sub-cycle 300 comprises:

pulsing a vaporized reducing agent, such as disilane or trisilane, intothe reaction chamber 310 to reduce at least some of the TiF₄ to TiF₃,

purging the reaction chamber 320 to remove excess reducing agent andreaction by products, if any,

providing a pulse of a nitrogen reactant, such as NH₃, into the reactionchamber 330, where the nitrogen reactant contributes at least somenitrogen to the titanium fluoride film,

purging the reaction chamber 340 to remove excess nitrogen reactant andany gaseous by-products, and

repeating 350 the pulsing and purging steps.

In some embodiments, the second reducing sub-cycle 300 is repeated 1, 2,3, 4, 5, 10, 20, 50, 100 or more times in succession. In someembodiments the second reducing sub-cycle is repeated about 3 to 6times, or about 5 times.

The first and second sub-cycles 200, 300 are repeated multiple times ina complete ALD super-cycle 100, and the complete ALD super-cycle 100 isrepeated to form a TiF₃ film of a desired thickness comprising a desiredconcentration of titanium, fluorine, and nitrogen.

In some embodiments, the number of times the first deposition sub-cycle200 and second reducing sub-cycle 300 are repeated is the same in eachcomplete ALD super-cycle 100. In other embodiments, the number of firstand second sub-cycles 100, 200 varies in one or more complete ALDsuper-cycles 100. The number of first and second sub-cycles 100, 200 ineach complete ALD super-cycle 100 and the total number of first andsecond sub-cycles 100, 200 and total ALD super-cycles 100 can beadjusted to achieve deposition of a TiF₃/TiN film of a desired thicknessand composition.

Although illustrated as beginning with the first deposition sub-cycle200, each complete ALD cycle may begin and end with either the first 100or second 200 sub-cycle. For example, each ALD super-cycle for formingthe TiF₃ film can be started with the first titanium fluoride depositionsub-cycle or the reducing sub-cycle. In some embodiments one or moresuper-cycles may begin with the reducing sub-cycle.

In some embodiments the film comprising TiF₃ is deposited by ALD over asubstrate surface to form a conformal thin film of 500 nm or less. Insome embodiments the thickness of the film is less than 100 nm, lessthan about 50 or less than about 10 . Depending on the application thethickness could be much less, such as when used as a p-type cappinglayer or oxidation prevention layer, and the thickness of the film couldbe for example, from about 2 to about 50 Å, preferably from about 3 toabout 30 Å and in some cases from about 5 to about 20 Å.

In some embodiments a film comprising TiF₃ is formed that only starts tooxidize in an oxygen or water/moisture-containing atmosphere, such asambient air at temperatures above about 300° C.

In some embodiments a film comprising TiF₃ film is formed that has an nof about 1.6-1.8 and a k value of about 0.1-0.2.

Various modifications, omissions and additions may be made to themethods and structures described above without departing from the scopeof the invention. All such modifications and changes are intended tofall within the scope of the invention, as defined by the appendedclaims.

EXAMPLES

A number of TiF₃ films were deposited by ALD in a Pulsar® 2000 R&Dreactor. The films were deposited with a super-cycle method using thefollowing basic super-cycle, comprising a TiF₄ sub-cycle and a reducingsub-cycle: z[x(TiF₄+y(Si₃H₈+NH₃)] and z[x(TiF₄+y(Si₂H₆+NH₃)]. Thereactor temperature was 350° C.

The basic process parameters were: TiF₄; 3 second pulse/5 second purge,NH₃; 10 second pulse/5 second purge, Si₂H₆/Si₃H₈; 1 second pulse/5second purge.

The films were deposited on silicon with native oxide. Film compositionswere altered by changing the TiF₄/reducing sub-cycle ratio (x/y) andfilm thicknesses were controlled by the number of super-cycles (z).

The films were characterized by four point probe measurements with CDEResmap 168 for sheet resistance, x-ray reflectivity (XRR) with Brüker D8Advance for thickness, roughness and density, by x-ray photoelectronspectroscopy (XPS) with PHI Quantum 2000 using monochromated AlK_(a) forcomposition (analysis done by EAG labs, East Windsor, N.J.), bysecondary electron microscope (SEM) with Hitachi S-4800 field emissionscanning electron microscope for morphology and conformality and byheated stage x-ray diffraction (XRD) with PANalytical X′Pert Pro MPDX-ray diffractometer with CuK_(a) radiation and HTK 1200 Anton Paar ovenin nitrogen and air atmospheres for crystallographic phase evolution asa function of annealing temperature.

The ALD processes resulted in films that contained a surprising amountof fluorine. XPS and XRD analysis revealed the films to be a mixture ofTiF₃ and TiN. The films were transparent and electrically conductive.Table 1 summarizes the composition, resistivity, roughness, density andgrowth rates of the processes with different TiF₄/reducing sub-cycleratios.

TABLE 1 Rs and ellipsometry data of TiF₄ + Si₂H₆/ Si₃H₈ + NH₃ withdifferent pulsing ratios. Sample 1 2 3 4 5 6 Reducing Agent Si₃H₈ Si₃H₈Si₃H₈ Si₂H₆ Si₂H₆ Si₂H₆ TiF₄/reducing 0.1 0.2 1 0.1 0.2 1 sub-cycleratio TiF₄/(TiF₄ + 0.09 0.17 0.50 0.09 0.17 0.50 reducing) sub-cycleratio Sub-cycles 440 360 400 440 360 400 Super-cycles 400 300 200 400300 200 Rs, Ω/sq — — 141000 20200 217000 263 (center point) LayerResistivity, — — 696540 88314 911400 822 μΩcm (center point) Layerthickness, 60.1 60.3 49.4 43.7 42.0 31.3 nm (3 mm EE, 21 points,average, ellipsometer) Layer Th Uf 10.6% 6.9% 17.2% 13.6% 14.4% 13.9% (3mm EE, 21 points, ellipsometer) Layer RI 1.66 1.63 1.75 1.83 1.83 2.02(average, 21 points, ellipsometer) N, at.-% 8.6 8 5.5 12.7 9.9 0.6 O,at.-% 0.6 0.9 0.6 0.9 0.6 2.1 F, at.-% 59.3 60.6 65 55 58.6 15.7 Si,at.-% 2.3 1.6 0.4 1.6 1 — Ti, at.-% 28.9 28.7 28.2 29.6 29.8 41.4

FIG. 2 illustrates an XRD pattern of the film of sample 3 of thisexperiment using Si₃H₈ as the reducing agent.

Films comprising TiF₃ were found to be much more resistant to oxidationthan TiN. The TiF₃/TiN films formed in the present experiment containedless than about 1 at % oxygen. Thermodynamic equilibrium calculationsshowed that the TiF₃/TiN mixture oxidization proceeds in ambient air(i.e., N₂, O₂, and H₂O) such that TiN is first oxidized (FIG. 3).

It was also determined that films comprising TiF₃ start to oxidize onlyat temperatures above 300° C. in an air ambient (FIG. 4). Without beingtied to any particular theory, it is believed that because the Ti—F bondis stronger than the Ti—O bond, TiF₃ exhibits greater resistance tooxidation than does TiN. The TiF₃ is believed to have an n and k ofabout 1.6-1.8 and 0.1-0.2, respectively.

In a separate example, Ti_(x)W_(y)N_(z) films were deposited by ALD in aPulsar® 2000 R&D reactor. The films were deposited with a super-cyclemethod using the following basic binary chemistries for TiN and W:z[x(TiCl₄+NH₃)+y(Si₂H₆+WF₆)]. The reactor temperature was 350° C. Thesteady state flow rates for Si₂H₆ and WF₆ were 100 sccm, and 240 sccmfor NH₃. TiCl₄ was filled in the liquid source, which was in vapor pushmode at room temperature (21° C.) and used N₂ as the carrier gas.

The basic process parameters were: TiCl₄; 50 ms pulse/5 s purge, NH₃; 10s pulse/5 s purge, Si₂H₆; 0.5 pulse/5 s purge and WF₆; 0.5 s pulse/5 spurge.

The films were deposited on 200 mm, 20 nm TiN/20 nm SiO₂/Si and 20 nmSiO₂/Si wafers and on 2 nm HfO₂/Si planar wafer pieces (≈10×10 cm) or onpatterned native SiO₂/Si (≈5×5 cm) pieces for conformality. The pieceswere placed on 200 mm adapter wafers during the deposition runs. Filmcompositions were altered by changing the TiN/W cycle ratio (x/y) andfilm thicknesses were controlled by the number of super-cycles (z).

The films were characterized by four point probe measurements with CDEResmap 168 for sheet resistance, x-ray reflectivity (XRR) with Brüker D8Advance for thickness, roughness and density, by x-ray photoelectronspectroscopy (XPS) with PHI Quantum 2000 using monochromated AlK_(a) forcomposition (analysis done by EAG labs, East Windsor, N.J.), bysecondary electron microscope (SEM) with Hitachi S-4800 field emissionscanning electron microscope for morphology and conformality and byheated stage x-ray diffraction (XRD) with PANalytical X′Pert Pro MPDX-ray diffractometer with CuK_(a) radiation and HTK 1200 Anton Paar ovenin nitrogen and air atmospheres for crystallographic phase evolution asa function of annealing temperature.

Table 2 summarizes the composition, resistivity, roughness, density andgrowth rates of the TiN/W mixed process with different TiN/W cycleratios. As can be seen in Table 2, the fluorine content of the filmsincreases with increasing TiN/W cycle ratios and decreasing roughness.

TABLE 2 Properties of the ALD Ti_(x)W_(y)N_(z) layers. The compositionsreported in the table are the compositions of the films measured by XPSafter sputtering with 2 keV Ar⁺ ions until the surface carboncontamination in the signals was absent. TiN/ Layer Layer TiN/W (TiN +W) Roughness, Density, Layer GR, N, O, F, Si, Ti, W, cycle cycle nmg/cm³ Resistivity, Å/sub- at.- at.- at.- at.- at.- at.- ratio ratio(RMS, XRR) (XRR) μΩcm cycle % % % % % % W 0 4.15 17.3 122.2 6.26 0.5 1.30.3 3.0 0.1 94.8 0.5 0.33 2.14 16.5 187.8 2.24 8.5 0.5 0.3 2.0 0.0 88.71 0.50 0.65 16.1 173.6 0.78 9.6 0.7 0.0 0.9 0.1 88.7 3 0.75 1.15 12.5622.3 0.77 21.0 0.6 3.0 1.0 3.1 71.4 5 0.83 1.96 11.9 711.4 0.63 25.70.4 3.0 1.2 7.2 62.4 20 0.95 1.01 8.6 553.7 0.33 39.9 0.3 2.3 0.5 24.932.0 40 0.98 0.65 7.8 381.6 0.30 44.0 0.6 1.6 0.8 32.2 20.8 TiN 1 2.745.3 143.1 0.24 53.2 0.8 0.0 0.2 45.7 0.0

Pure W films grew with a high growth rate of 6 Å/cycle, comparable tothe growth rates reported in the literature on Al₂O₃. However, theroughness of the W film was also very high. Adding some TiN cycles inbetween the W cycles decreased the growth rate of the films and at thesame time the roughness of the film was reduced substantially.Surprisingly though, the films did not contain any titanium when theTiN/W cycle ratio was ≤1. Instead, the resultant film was W_(x)N_(y)with less than 10 at % nitrogen and some silicon impurity. This mayindicate that the TiN cycles in between the W cycles modified thenucleation behavior of W and resulted in lower growth rates and smootherfilms.

When the TiN/W cycle ratio was increased to ≥3, the films started toshow a further increase in nitrogen content and a slow increase intitanium content with an increasing TiN/W cycle ratio. This suggestedthat when an adequate amount of TiN cycles was done before the W cycle,the Si₂H₆ and WF₆ was not able to remove all the titanium from thesurface and therefore the titanium content of the films graduallystarted to increase.

The resistivity of the films first increased with increasing nitrogencontent when the titanium content of the film was low, and then startedto decrease again when the titanium content of the films was more than≈20 at %.

The crystallographic phases of the films were studied by x-raydiffraction analysis. Pure W films showed (β-W crystal structure. Thestabilization of the metastable β-W phase for the pure ALD tungsten hasnot been reported before. In order to determine whether the β-Wstabilization is a general result of the ALD W process itself, or if itwas stabilized by the HfO₂ substrate, the pure W process was also run onTiN and SiO₂ substrates. These results are presented in FIGS. 5A-C,which show XRD patterns of 100 cycles of pure ALD-W films deposited onTiN (FIG. 5A), SiO₂ (FIG. 5B) and HfO₂ (FIG. 5C) surfaces. The XRD peakshifts to higher 20-values indicate that the films have residual tensilestress in all cases. The peak intensity increase in FIG. 5A is causedmainly by the increased grain size with higher deposition temperatureand partly because of the higher growth rate with higher depositiontemperature. At 150° C. there was no film growth on the TiN surface

The TiN substrate was found to promote the stabilization of β-W crystalstructure, whereas on SiO₂ substrates the resultant film seemed to beα-W with small crystallite size, as indicated by the wide XRD 2⊖ peak at≈40°. In all cases, the XRD 2⊖ peaks were shifted to higher 2⊖ valuescompared to the powder diffraction reference values, indicating that thetungsten film had tensile residual stress on all the surfaces. However,the shift was greater for the β-W on TiN and HfO₂ than for the α-W onSiO₂. The α-W to β-W transition may also partly explain the higher ALDgrowth rates (≈6 Å/cycle) for W observed on TiN and HfO₂ and what hasalso been reported in the literature on Al₂O₃, compared to the growthrates reported on SiO₂ (≈3 Å/cycle). β-W has a lattice parameter of 5.05Å, whereas for α-W it is 3.16 Å.

FIGS. 6A and B show the results for deposition of mixed Ti_(x)W_(y)N_(z)films on HfO₂. With TiN/W cycle ratios of less than 3 the XRD analysisrevealed two very wide peaks at 40 and 70°. These peaks could not beassigned to any of the compounds containing W and N in the XRD database;however their position matches the β-W peaks, so it is possible thatthese films still have the crystal structure of β-W, but have anextremely small crystallite size.

The Ti_(x)W_(y)N_(z) films formed with TiN/W cycle ratios 3≤5 (Ticontent 3≤7 at %) adapted the crystal structure of W₂N with tungstenatoms randomly displaced by titanium atoms in the lattice. For TiN/Wcycle ratios between 3 and 5, the W₂N peaks in the Ti_(x)W_(y)N_(z)films were visible, but with 2 theta values shifted in between the W₂Nand TiN peaks. Also the intensity ratios of the XRD peaks changed withthe composition of the Ti_(x)W_(y)N_(z) layer. This type of behavior inthe XRD pattern is typical for a solid solution.

With larger TiN/W cycle ratios the XRD peaks are shifted closer to theTiN peaks. In the case of the films deposited using TiN/W cycle ratios≥20 (Ti content ≥25 at %), the films adapt the crystal structure of TiNwith titanium atoms randomly displaced by tungsten atoms in the lattice.

Both W_(x)N_(y) and Ti_(x)W_(y)N_(z) films exhibited substantially widerXRD peaks than pure W or TiN films with comparable thicknesses. Thegrain size estimated with the Debye-Scherrer method was ≈2 nm forW_(0.9)N_(0.1) (1:1 TiN/W cycle ratio) and ≈20 nm forTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) film. FIG. 7 presentsa comparison of the morphology of the W_(x)N_(y) and Ti_(x)W_(y)N_(z)layers deposited at various TiN:W sub-cycle ratios, along with pure Wand TiN. The columnar grain structure clearly visible in pure W and TiNfilms is absent in the SEM images of the mixed process films. Thisconfirms that the smooth film surfaces modeled in the XRR analysis andthe wide peaks in the XRD patterns are a consequence of thenanocrystalline phase of the mixed process films with no visible grainmorphology in the SEM analysis.

FIG. 8 presents a SEM image of a W_(0.9)N_(0.1) (1:1 TiN/W cycle ratio)film in a 3D trench structure. The true ALD nature in the growth of thefilm is evident within the trench, showing constant film thicknessinside the trench even though the trench width increased with its depth.

The stability and oxidation resistance of the nanocrystalline phase of aternary Ti_(x)W_(y)N_(z) film with a composition ofTi_(0.26)W_(0.33)N_(0.41) (20:1 TiN/W cycle ratio) was studied by heatedstage XRD. In nitrogen atmosphere the nanocrystalline phase was stableat up to 875° C. with no sign of grain coarsening during the heatingcycles as shown in FIG. 9A. FIG. 9B shows a comparison with a pure TiNfilm with a similar thickness. FWHM was ≈0.7° forTi_(0.26)W_(0.33)N_(0.41) and ≈0.4° for TiN. This result suggests thatthe theoretically predicted high thermodynamic stability of thenanocrystalline phase in Ti—W alloys may be true also for the Ti—W—Nsystem. Grain size estimated with the Debye-Sherrer method was about 20nm for a 40 nm thick Ti_(0.26)W_(0.33)N_(0.41) film.

Further testing was performed comparing the oxidation resistanceachieved by TiWN thin films to that achieved by TiN films. Using an ALDprocess as disclosed herein, TiWN films were grown producingnanocrystalline metallic films with higher oxidation resistance thanachieved with ALD-deposited TiN films. In particular, the TiWN filmswere deposited by ALD from x sub-cycles of TiCl₄ and NH₃ and ysub-cycles of Si₂H₆ and WF₆. Table 3 below illustrates the oxidationresistance of TiWN thin films deposited with a cycle ratio of 20:1 (x:y)and 40:1 (x:y), compared to the oxidation resistance of pure TiN filmsat the same three nominal thicknesses.

TABLE 3 Rs before and after oxidation of thin TiWN and TiN films NominalXRR thickness Rs as Rs after O₃ Rs after O₃ Estimated oxide Estimatedoxide thickness as deposited deposited exposure* exposure** thicknessafter O₃ thickness after O₃ Material (nm) (nm) (Ω/sq) (Ω/sq) (Ω/sq)exposure* (nm) exposure** (nm) TiN 5.0 5.1 468 N/A N/A 5.1 5.1 7.0 7.1232 N/A N/A 7.1 7.1 9.0 9.1 152 4305 N/A 8.8 9.1 TiWN 5.0 5.2 2063 N/AN/A 5.2 5.2 20:1 7.0 7.2 1197 220000  N/A 7.2 7.2 9.0 8.7 900 2384 24985 5.4 8.4 TiWN 5.0 5.3 1377 N/A N/A 5.3 5.3 40:1 7.0 7.8 7101643000   N/A 7.8 7.8 9.0 8.8 584 2874 120000 7.0 8.8 *O₃ exposureconditions: 250 g/Nm³, 500 sccm, 400° C., 15 min. **O₃ exposureconditions: 250 g/Nm³, 500 sccm, 400° C., 30 min.

It can be seen that TiWN oxidizes slower than TiN. Without beingrestricted to any particular theory, this is believed to be caused bythe more nanocyrstalline structure of the TiWN films compared to TiN.Because the TiWN films exhibits no columnar structure, they experienceslower oxygen diffusion inside the film. Additionally, the fluorinecontent in the TiWN films resists diffusion of oxygen. The surface ofthe TiWN films is enriched in fluorine compared to the bulk of the film.And the oxidation of the fluoride (i.e., 2TiF₃+2O₂

2TiO₂+F₂) is a thermodynamically unfavorable reaction.

Although certain embodiments and examples have been discussed, it willbe understood by those skilled in the art that the scope of the claimsextend beyond the specifically disclosed embodiments to otheralternative embodiments and/or uses and obvious modifications andequivalents thereof.

We claim:
 1. An atomic layer deposition (ALD) process for depositing afluorine-containing thin film on a substrate, the process comprising aplurality of super-cycles, each super-cycle comprising a first sub-cycleand a second sub-cycle, wherein: the first sub-cycle comprisescontacting the substrate with a metal fluoride; and the second sub-cyclecomprises alternately and sequentially contacting the substrate with areducing agent and a nitrogen reactant, and wherein the plurality ofsuper-cycles forms a continuous fluorine-containing thin film having alayer resistivity of less than about 10⁶ μΩcm on the substrate.
 2. Theprocess of claim 1, wherein the metal fluoride comprises a metalselected from Ti, Ta, Nb, Mo and W.
 3. The process of claim 1, whereinthe fluorine-containing thin film comprises TiF₃ and TiN.
 4. The processof claim 1, wherein the fluorine containing thin film comprises TiF₃. 5.The process of claim 4, wherein the thin film comprises about 5 to about40 at % nitrogen.
 6. The process of claim 1, wherein thefluorine-containing thin film is conductive.
 7. The process of claim 1,wherein the fluorine-containing thin film is not oxidized by an airambient at less than about 300° C.
 8. The process of claim 1, whereinthe metal fluoride comprises TiF₄.
 9. The process of claim 1, whereinthe reducing agent is a silane or borane.
 10. The process of claim 9,wherein the reducing agent comprises disilane or trisilane.
 11. Theprocess of claim 1, wherein the nitrogen reactant is selected from thegroup consisting of ammonia, N₂H₄, nitrogen atoms, nitrogen containingplasma and nitrogen radicals.
 12. The process of claim 1, wherein thefirst sub-cycle and the second sub-cycle are carried out at a ratio ofat least about 0.1 in at least one of the plurality of super-cycles. 13.An atomic layer deposition (ALD) process comprising: conducting aplurality of super-cycles to form a continuous fluorine-containing thinfilm having a resistivity of less than about 10⁶ μΩcm, each super-cyclecomprising a first sub-cycle and a second sub-cycle, and wherein: thefirst sub-cycle comprises contacting the substrate with a metalfluoride; and the second sub-cycle comprises contacting the substratewith a nitrogen reactant; wherein at least one of a silane compound anda borane compound is separately provided in at least one of the firstsub-cycle and the second sub-cycle.
 14. The process of claim 13, whereinat least one of a silane compound and a borane compound is provided inthe first sub-cycle.
 15. The process of claim 13, wherein at least oneof a silane compound and a borane compound is provided in the secondsub-cycle.
 16. The process of claim 13, wherein the fluorine-containingthin film has a thickness of less than about 100 nm.
 17. The process ofclaim 13, wherein at least one of the silane compound, borane compound,and nitrogen reactant reduces at least some of the metal of the metalfluoride.
 18. The process of claim 13, wherein the fluorine-containingthin film exhibits substantially no oxidation at temperatures belowabout 300° C.
 19. The process of claim 1, wherein thefluorine-containing thin film comprises TiF₃ and TiN.
 20. The process ofclaim 1, wherein the fluorine-containing thin film comprises TiF₃.